1. In some sheets of epithelial tissue, the cells are joined together with dense membrane proteins that form "tight junctions," which are extremely impermeable (see Chapter 5). In other epithelial sheets, the cells are joined by filamentous extracellular proteins that are strong, but not as impermeable. Where in the body might you expect to find tight junctions? Where might you expect to find epithelial sheets with the leakier connections?
2. If the major adaptation of endotherms to cold climates is their insulation, how would you compare the cold adaptations of a polar bear and a seal?
3. Why is an environment above its upper critical temperature more dangerous to an endotherm than an environment below its lower critical temperature?
4. If the hypothalamic temperature of a mammal is the feedback information for its thermostat, why does the hypothalamic temperature scarcely change when that animal moves between environments hot enough and cold enough to stimulate the animal to pant and to shiver, respectively?
5. There are many places on Earth where cold is a severe challenge to life. Therefore, if global warming occurs, wouldn't it expand the habitats available to many species? What arguments can be advanced to support or rebut this simple proposition?
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.